Could turning genes on and off explain the Hulk and Captain America? Scientists have already attempted to explain Hulk's super anger and Captain America's invulnerable shield in broad terms, but now Stanford biologist Sebastian Alvarado offers an explanation for their superpowers that is consistent with their canonical origin: epigenetics.

Alvarado, who is also involved with the Avengers S.T.A.T.I.O.N. in New York City, explains that, although they have very different origin stories, the powers of Captain America and Hulk can both be explained by epigenetics, or changes in gene expression that result from flipping genes' on/off switches, so to speak.

(Credit: Marvel)

Captain America was created when a sickly, 90-pound fine arts student named Steve Rogers tried and failed to join the Army. The government then uses him as a test subject for "Project: Rebirth," and injects him with a serum meant to turn him into a super-soldier. The serum is successful, and turns him into a nearly perfect human specimen with enhanced strength, stamina, and intelligence. According to Alvarado, there is no serum that can perform this feat yet, but scientists could potentially create this type of enhanced human by selectively turning genes off and on.

"We have a lot of genome-editing tools – like zinc finger nucleases, or CRISPR/Cas9 systems – that could theoretically allow you to epigenetically seek out and turn on genes that make your muscles physically large, make you strategically minded, incredibly fast, or increase your stamina," Alvarado said. And, similar to the Project: Rebirth serum, these epigenetics tools can be packaged into capsules.

In order to activate the serum, Steve Rogers was also exposed to the fictional type of radiation called Vita Rays. Alvarado claims that this is possible as well, as the real-life capsules can be activated by certain wavelengths, such as ultraviolet light. Although we don't know the exact wavelength of Vita Rays, it should theoretically be easy to modify the capsules in order to make them activate in response to the Vita Rays wavelength.

(Credit: Marvel)

Speaking of radiation exposure, Alvarado also explains the science behind the Hulk's origin story, in which he goes from a mild-mannered scientist to a mild-mannered scientist who occasionally transforms into a giant green brute after exposure to gamma radiation. (His explanation could likely apply to many superheroes, as radiation exposure is a staple of superhuman origin stories. Besides the Hulk, there's Spider-Man, Dr. Manhattan, Daredevil, the Fantastic Four, the list goes on and on.) He explains that his transformation could be the result of chromothripsis, or chromosomal shattering, the process by which radiation breaks the DNA strand in several places. Usually, a few minor breaks will be automatically repaired without significant changes to one's gene expression. But in the case of a huge gamma ray explosion, the breaks could be numerous enough that the repairs lead to epigenetic changes. And, although he admits this is a bit of a stretch, it's possible that the changes could be activated by the hormones produced in the body when Bruce Banner gets angry, instead of being triggered by certain types of light.

He also offered an explanation for the Hulk's skin turning green: when the body undergoes a trauma, the skin turns green as a result of red blood cell death. The death of a red blood cell causes the metabolization of hemoglobin, and one of the metabolites of hemoglobin is a molecule called biliverdin, which causes the blood to appear green under the skin. There are examples of this in the animal kingdom as well; many lizards with a higher concentration of biliverdin have blood that appears entirely green.

"Bruce Banner's transformation into the Hulk would be incredibly traumatic to his body, and maybe his green skin is the result of a whole-body bruise," Alvarado said. "If you want to get really creative, maybe his blood is full of some sort of green Hulk-oglobin, which can carry more oxygen to the muscles than hemoglobin and gives him his strength and stamina."

He concludes his analysis with the old joke: "If there's one mystery that science just can't solve, it's how his pants stay on after every transformation."